474 Prof. T. R. Lyle on 



Its details are as follows : — 



Core : — 144 annular laminae annealed and paper insulated. 



Lamina?:' — Internal diameter 15*25 cm. 



External diameter 27*75 cm. 



Thickness "047 cm. 



Primary coil : — No. of turns (nJ^lOO. 



Resistance (warm) = 0*0676 ohm. 

 Secondary coil: — No. of turns (n 2 ) = 600. 



Resistance (warm) = 2*034 ohms. 



Before either coil was wound a single turn of well-insulated 

 wire was looped on the core to serve as a search-coil for the 

 determination, by means of the wave-tracer, of the magnetic 

 flux pulsating in the core. The secondary coil was wound 

 next the core. 



The primary current was drawn from the alternating side 

 of a small rotary converter that was supplied with direct 

 current from storage-cells. The spindle of the commutator 

 and that of the converter were in line and rapidly connected 

 so that perfectly synchronous commutation was obtained. 

 A chronograph took a continuous record of the period, re- 

 cording once every 200 alternations. 



The arrangement of the transformer and the mutual in- 

 ductances by means of which the different waves were 

 determined is shown in fig. 1. The primary current Q x 

 from the converter enters by the two leads marked Cj. In 

 one of these leads is placed a two-pole switch a 1? by which 

 C\ can be sent through the primary p x °£ f ne triad T, or 

 deflected through an equal compensating coil b l9 leaving p x 

 completely disconnected from the live circuit in case the 

 triad is being used for the determination of C 2 . 



E, is determined by obtaining the trace of the current wave 

 it sends through a non-inductive resistance of 1220 ohms. 

 The mutual inductance m ± of "00061 henry is used for ob- 

 taining this trace. E 2 is similarly determined, the non- 

 inductive resistance in circuit being 8660 ohms and the 

 mutual inductance m 2 '003535 henry. 



The secondary current C 2 may, by means of the switch a 2 , 

 be directed through the primary p 2 of the triad T or through 

 the equal compensating coil b 2 . When n 1 G 1 ^-n s G a \s being 

 determined, both C x and C 2 flow through their respective 

 primaries p l9 p 2 of the triad in the proper relative directions, 

 the common secondary s being joined as shown to the com- 

 mutator and thence through a resistance to the galvanometer. 

 When C 1 alone is being determined, C 3 is deflected through 

 its compensating coil b 2 ; similarly when C 2 alone is being 



